1. Field of the Invention
The present invention relates to a color liquid crystal display device capable of displaying uniformly four colors of white, red, blue and green in a state of highly purified color development by multiplex driving.
2. Background Art
JP-A-2-118516 (conventional example 1) discloses that it is possible to obtain a large variation of colors by changing a voltage applied to a liquid crystal cell containing twisted liquid crystal. However, the disclosed technique has a problem that color development is limited to only yellow, red, purple, violet, blue and green, and a white display is impossible.
Further, the conventional example 1 discloses a two-layered structure using a compensation cell whereby a monochrome display is possible. However, it has a problem that it is impossible to display uniformly white or black or a color such as blue, green or the like on a picture surface.
JP-A-2-183220 (conventional example 2) discloses that pixels are formed even in the compensation cell to effect a display wherein white or black and colors of blue, green and so on can uniformly be displayed. In this technique, however, there are problems that pixels in the two-layered liquid crystal panels must be formed in a one-to-one corresponding relation, which makes the manufacture very difficult, and when a picture displayed on the layered liquid crystal panels is observed from an oblique direction, parallax appears whereby complete overlapping of colors can not be expected. Further, there is a further problem of increasing the weight of the device.
JP-A-8-292434 (conventional example 3) describes that an achromatic color can be displayed by using a retardation plate as well as being capable of developing blue, red and green. In this technique, however, a color development of red subsequent to white obtained by applying a voltage is orange red, and it is impossible to develop a color of red having a high color purity.
Although the conventional example 3 describes the way of developing a color of pink red where visibility to red is high, this technique requires an increase of xcex94nLdL of liquid crystal to enhance a change of condition of liquid crystal so that pink red is developed. In order to display uniformly pink red and white by multiplex driving, it was necessary to render xcex94nLdL of a liquid crystal layer to be 1.7 or more. However, there was a limit in increasing xcex94nLdL of the liquid crystal layer by increasing xcex94nL. Further, it was necessary to increase dL. Accordingly, there were problems that the response speed of liquid crystal was low; view angle dependence became large; the structure became weak due to an increase of the cell gap, and temperature dependence became large. Therefore, the conventional example 3 is not practical.
Thus, the conventional example 3 could not provide white of high purity and red where visibility to red is high even by adjusting practical xcex94nLdL of a liquid crystal layer.
JP-A-9-33917 (conventional example 4) discloses that when a liquid crystal layer having xcex94nLdL of 1.533 xcexcm is driven by a static driving system and a polarizer colored with a blue series color is used, a display of red color composed of a pink series orange is obtainable as well as a display of four colors of an achromatic color, red, green and blue, and in addition, when a polarizer colored with a purple series color is used, red is strong.
Even in this method, however, it is impossible to display of red, white, blue and green each having high purity by multiplex driving.
It is an object of the present invention to provide a color liquid crystal display device capable of displaying uniformly four colors of white, red, blue and green with high purity by multiplex driving.
In accordance in a first aspect of the present invention, there is provided a color liquid crystal display device capable of developing colors of white, red, blue and green with a same display unit, which comprises:
a liquid crystal layer held between two substrates arranged substantially in parallel to each other, each provided with a transparent electrode and an aligning layer wherein the liquid crystal layer is composed of a nematic liquid crystal; the twist angle of the liquid crystal layer, according to the alignment direction of liquid crystal molecules, determined by the alignment layers on the substrates is 160-300xc2x0 and the product xcex94nLdL of the refractive anisotropy xcex94nL of the liquid crystal in the liquid crystal layer and the thickness dL of the liquid crystal layer is 1.0-1.5 xcexcm,
a pair of polarizers disposed outside the liquid crystal layer wherein at least one of the pair of polarizers is a color polarizer; and the wavelength dependence of the polarizing efficiency of the color polarizer is 0.1-0.7 in terms of (the polarizing efficiency of a wavelength of 650 nm)/(the polarizing efficiency of a wavelength of 450 nm), 0-0.6 in terms of (the polarizing efficiency of a wavelength of 650 nm)/(the polarizing efficiency of a wavelength of 550 nm) and 0.4-1.0 in terms of (the polarizing efficiency of a wavelength of 450 nm)/(the polarizing efficiency of a wavelength of 550 nm); and a driving circuit for applying a driving voltage across the transparent electrodes, which conducts multiplex driving to enable the selection of at least four different voltage values.
According to a second aspect of the present invention, there is provided the color liquid crystal display device according to the first aspect wherein the wavelength dependence of the polarizing efficiency of the color polarizer is 0.2-0.6 in terms of (the polarizing efficiency of a wavelength of 650 nm)/(the polarizing efficiency of a wavelength of 450 nm), 0.1-0.6 in terms of (the polarizing efficiency of a wavelength of 650 nm)/(the polarizing efficiency of a wavelength of 550 nm) and 0.5-1.0 in terms of (the polarizing efficiency of a wavelength of 450 nm)/(the polarizing efficiency of a wavelength of 550 nm).
According to a third aspect of the present invention, there is provided the color liquid crystal display device according to the first aspect or the second aspect, wherein the angle xcex82 formed between the direction of stretching axis of a retardation plate and the orientation direction of liquid crystal molecules at the side of the substrate on which the retardation plate is disposed is 80-100xc2x0; the angle xcex81 formed between the absorbing axis of the polarizer adjacent to the retardation plate and said orientation direction is 130-150xc2x0 and the angel xcex83 formed between the direction of absorbing axis of the polarizer at the side of the other substrate and the orientation direction of liquid crystal molecules at the side of the other substrate is 125-145xc2x0.
According to a fourth aspect of the present invention, there is provided the color liquid crystal display device according to any one of the first to third aspects, wherein a reflection plate or a transflector is disposed at an outer side of the other polarizer between the pair of polarizers.
Further, according to a fifth aspect of the present invention, there is provided the color liquid crystal display device according to any one of the first to fourth aspects, wherein xcex94nL of the liquid crystal is at least 0.18.